Above a certain intensity of the optical irradiation, a photovoltaic solar cell supplies an electric current that rises with the irradiation intensity. Already above a low irradiation intensity, a voltage is present via the solar cell. The current is drawn in the conventional manner via the current connections of a terminal box. The short-circuit current of a solar cell and thus also of a solar module is only negligibly higher (approximately 5%) than is the case with the rated current supplied in conjunction with the appertaining irradiation. Solar modules consist of a plurality of serially connected photovoltaic solar cells. Solar modules, in turn, are generally serially connected to form a solar array in order to supply a sufficiently high voltage (if applicable, up to 1000 V) to an AC-DC inverter. For safety reasons, the connection of the solar array to the AC-DC inverter can be separated by a direct voltage disconnector switch. In order to increase the performance, a plurality of solar arrays can be connected in parallel or via separate inputs with the interposition of appropriate direct voltage disconnector switches. However, the presence of the direct voltage disconnector switch(es) does not mean that, during exposure to irradiation, a given individual solar module is voltage-free during the assembly of a solar energy installation, during maintenance or repair work, in case of a malfunction or in case of fire, but rather, an open-circuit voltage is indeed present at the current connections of the solar module, causing hazardous touch voltages to occur in the solar energy installation.
According to German patent application DE 10 2006 034 223 A1, the solar module contains a bypass diode that bridges the serially connected solar cells. When the solar module is exposed to solar irradiation, that is to say, when the solar module is generating current, the bypass diode is polarized in the non-conducting direction and thus has no effect on the function of the solar cells. If the solar module within a solar array is temporarily inactive, especially due to shading, this solar module, which is now de-energized, no longer generates voltage, and the bypass diode draws the current for the array from the other solar modules within a solar array. The shaded solar module is protected against damage due to overheating, and the function of the solar array is retained. The bypass diode functions in an analogous manner in case of a defective solar module, and the functionality of the remaining solar array is retained.
According to German patent application DE 10 2006 026 661 A1, in case of a shaded or defective solar module, the power dissipation of the solar module is reduced in that, instead of the bypass diode, a semiconductor switching element is provided that has a low forward voltage, that is blocked by control electronics when the solar module is generating current, and that otherwise is switched with a low resistance. It is a drawback that the current supplied by the solar module is diminished by the current consumed by the control electronics. Moreover, here as well, there is no protection against touch voltages.
German patent DE 10 2005 017 835 B3 describes a photovoltaic generator with a thermal switching element that, when activated, short-circuits the module connection poles or the array connection poles or the connected AC-DC inverter.
German patent DE 10 2005 018 173 B3 describes a switching device for reliably interrupting the operation of photovoltaic installations, whereby the switching device has a protection means that, via a control line, can switch the generator field to a low-energy operating point. In this context, the triggering mechanism connected to the control line is far away from the protection means.